The need for a suitable classification of media types arises for several reasons when building or comparing multimedia systems. Within an Intelligent Multimedia Presentation Systems (IMMPS), it is necessary to formulate and encode design knowledge for decision making on the appropriate medium in which to present information and for the generation of the presentation. It is also required in order to specify interfaces to and between system components which will be employed to run a generated presentation before the user's eyes. This task is reflected in the Standard Reference Model (SRM, see this volume) for IMMPS by the Presentation Display Layer. However, the SRM does not instantiate this layer in detail, but instead refers to the Presentation Environment for Multimedia Objects (PREMO) ISO/IEC standard which provides a reference model for a presentation runtime environment for multimedia. PREMO already contains a set of basic structures, the so-called PREMO Primitive Hierarchy, to describe different media types. Thus the question arises, as to how far the PREMO Primitive Hierarchy could serve as a media classification for the SRM in general. In particular, this would support consistency between the design and presentation layers of the SRM if PREMO were used to instantiate the presentation layer. In the current paper, we first point to a number of typical problems with generating classifications of media types. We then provide a brief introduction to PREMO and its Primitive Hierarchy. Finally, the benefits and costs of using the PREMO Primitive Hierarchy for the SRM are discussed.